反应烧结Cr/Si/C复相陶瓷的微观结构表征与力学性能

本文采用掺杂Cr2C3的方法探究增韧补强反应烧结SiC陶瓷的途径。通过凝胶注模成型及反应烧结工艺制备Cr/Si/C复相陶瓷由SiC、Si和CrSi2组成,CrSi2由Cr2C3与熔融Si反应生成;材料中SiC颗粒分布均匀,CrSi2存在明显偏析;Gr/Si/C复相陶瓷抗弯强度接近反应烧结SiC/Si陶瓷,平面应变断裂韧性KIC达到3.81MPa.m1/2;CrSi2分布不均和弱化界面结合是抗弯强度以及弹性模量降低的原因。     

液相烧结SiC基复合材料的组织与力学性能研究

以α-SiC和BaAl2Si2O8（BAS）为原料,采用热压烧结工艺制备了SiC基复合材料．研究了添加剂对液相烧结SiC基复合材料的致密化、显微组织、抗弯强度及断裂行为的影响．测试结果表明,添加剂BAS有效促进了SiC基复合材料的致密化．40wt％BAS／SiC复合材料的抗弯强度和断裂韧性分别高达454MPa和5．1MPa·m^1/2．复合材料的主要增韧机制为SiC晶粒的拔出、裂纹偏转和裂纹桥连．     

陶瓷/Mg_2Si纳米复合材料制备及力学性能研究

以纳米陶瓷颗粒Si3N、AlN和常规Mg、Si粉为原料,采用机械合金化和真空热压相结合的方法制备Si3N/Mg2Si和AlN/Mg2Si纳米复合材料,并对样品的微结构和力学性能进行了表征。结果表明:随着纳米陶瓷颗粒体积分数由0%增加到20%,金属间化合物Mg2Si的硬度得到了很大的提高,Si3N/Mg2Si纳米复合材料的断裂韧性由0.59MPa·m-1/2增加到1.38MPa·m-1/2,而AlN/Mg2Si的断裂韧性却基本不随AIN的含量增加而改变。     

环境功能材料羟基磷灰石改性的研究进展

羟基磷灰石（HAP）有特殊的晶体化学特征，有良好的离子吸附和交换性，是一种新型的环境功能材料。通过制备方法的优化和新型处理技术对HAP改性．使HAP得到细化、均化、活化的作用．达到纳米级材料，提高了它的吸附性能，在环境治理领域具有良好应用前景。本文综述了HAP环境功能材料改性的研究进展，并对其提出了相应的设想和展望。     

C eO 2掺杂对 PZT 压电陶瓷介电性能的影响

为了提高Pb（Zr0．52 Ti0．48）O3（PZT）压电陶瓷的性能,通过改进传统固相法,研究CeO2不同掺杂量对PZT压电陶瓷性能的影响。采用X射线衍射和阻抗分析仪对样品进行分析,研究结果表明,掺杂后的PZT压电陶瓷均为单一的钙钛矿结构,随着掺杂量的增加,晶相逐渐从四方相向三方相转变,相对介电常数和介电损耗先增加后减少。当CeO2掺杂质量分数为0．6％时,介电常数达到最大值,为934;掺杂质量分数为0．8％时,介电损耗最小,为1．3％。这表明了CeO2掺杂既可以是“软性”掺杂,又可以是“硬性”掺杂。     

YSZ/Al_2O_3复合陶瓷的制备及性能研究

选用ZrO2（5wt．％Y2O2）和Al2O2为粉体原料,采用溶胶凝胶法制备氧化锆基氧化铝（YSZ／Al2O3）复合陶瓷,研究了悬浮体的Zeta电位、分散性、流变性及其显微结构．结果表明：在pH=9～10附近、选用SD-00为分散剂,加入量为1．0wt．％,粉体最佳配比为70wt．％ZrO2（5wt．％Y2O2）和30wt．％Al2O3获得固相含量为50Vol．％的悬浮体,制备出了均匀致密、高强度的YSZ／Al2O3复合陶瓷．     

Al2TiO5-Al2O3复相陶瓷的研究

利用一次烧成和二次烧成两种方法制备了Al2TiO5-Al2O3复相陶瓷,研究了Al2TiO5-Al2O3复相陶瓷的烧结工艺和原料组成对其性能的影响．研究结果表明：Al2TiO5-Al2O3复相陶瓷的组成和烧成工艺对其性能具有重要影响．利用一次烧成制得的Al2TiO5-Al2O3复相陶瓷的综合性能优于二次烧成．一次烧成组成为80wt％氧化铝和20wt％钛酸铝的复相陶瓷,其吸水率仅有0．11％,显气孔率为0．32％,体积密度为3．00g·cm^-3,弯曲强度达152．88MPa,热膨胀系数为7．5×10^-6/℃．     

H2S／air固体氧化物燃料电池的性能研究

采用陶瓷薄膜技术及溶胶一凝胶法制备了氧离子传导YSZ（Y2O3稳定的ZrO2）电解膜与电极催化剂,构建了膜电极组装（MEA）及结构为H2S、（复合MoS2阳极）／YSZ传导膜／（复合NiO阴极）、空气燃料电池系统;通过在MoS2中掺杂NiS、电解质、Ag粉和淀粉制备了双金属复合MoS2阳极催化剂,在NiO中添加电解质、Ag粉和淀粉制备了复合NiO阴极催化剂：考察了不同操作温度对电池性能的影响,比较了几种不同电极催化剂的性能,研究了H2S／air固体氧化物燃料电池的电化学性能。实验结果表明,在H2S环境中,复合MoS2阳极催化剂比MoS2和Pt具有更好的性能,复合Nio阴极Pt阴极的极化小;在电极催化剂中加入Ag可显著提高电极的导电性．添加电解质和淀粉可以提高电极的离子传导性和多孔性：操作温度增加．传导膜的电传导率和电化学反应速率增加,电池的输出电流与功率密度增加,电化学性能变好。电池连续运行1～4d几乎不降级。在850℃和101．13kPa时．燃料电池最大输出功率密度为155mW·cm^-2,对应的电流密度为240mA·cm^-2。     

压电生物陶瓷人工骨材料合成工艺研究

根据电场能促进骨细胞生长这一生物学特点,设计一种新型的既能填充骨缺损又能刺激骨细胞形成的仿生人工骨材料,从众多的压电陶瓷中选取BaTiO3、从活性生物材料中选取Ca3（PO4）2为主要原料,辅以助熔剂、成孔剂等添加剂,合成压电相与磷酸三钙复合型生物陶瓷人工骨（BTTCP）,确定合适的制备工艺,并用XRD、SEM、EPMA等现代测试手段对其组成、性能及微观结构的关系进行探讨和分析,为骨缺损的修复探索一条新途径.     

纳米TiO_2对离心自蔓延复合钢管组织性能的影响

为了提高离心-SHS复合钢管的致密度及力学性能,针对Al-Fe_2O_3铝热体系,在铝热剂中添加质量分数6%SiO_2、4%Na2B4O7,采用离心自蔓延高温合成法制备出陶瓷内衬复合钢管,研究不同质量分数的纳米TiO_2添加剂对复合钢管组织结构及力学性能的影响。XRD分析表明,陶瓷层的主要成分为α-Al_2O_3,还有少量Al_2SiO_5,B_2O_3存在。SEM观察发现陶瓷层表面无裂纹、致密度良好。力学实验结果表明,加入8%(质量分数)纳米TiO_2的陶瓷层的压剪强度及复合钢管的压溃强度分别达到13.5 MPa和525 Mpa,测试结果表明致密度可达94.2%。     

Microstructures and mechanical properties of SiBCNAl ceramics produced by mechanical alloying and subsequent hot pressing

Amorphous SiBCNAl powders were prepared via a mechanical alloying (MA) technique using crystalline silicon (Si), hexagonal boron nitride (h-BN), graphite (C), and aluminum (Al) as starting materials. SiBCNAl powders were consolidated by a hot pressing (HP) technique at 1800 °C under a pressure of 30 MPa in argon and nitrogen. The sintering atmosphere had a great influence on the microstructures and mechanical properties of the ceramics. The two ceramics had different phase compositions and fracture surface morphologies. For the ceramics sintered in argon, flexural strength, fracture toughness, elastic modulus and Vickers hardness were 421.90 MPa, 3.40 MPa·m1/2, 174.10 GPa, and 12.74 GPa, respectively. For the ceramics sintered in nitrogen, the mechanical properties increased, except for the Vickers hardness, and the values of the above properties were 526.80 MPa, 5.25 MPa·m1/2, 222.10 GPa, and 11.63 GPa, respectively.     

Microstructure and mechanical properties of liquid phase sintered silicon carbide composites

Silicon carbide (SiC) composites were prepared by hot-press sintering from α-SiC starting powders with BaAl2Si2O8 (BAS). The effects of additives on densification, microstructure, flexural strength, and fracture behavior of the liquid phase sintered (LPS) SiC composites were investigated. The results show that the served BAS effectively promotes the densification of SiC composites. The flexural strength and fracture toughness of the SiC composites can reach a maximum value of 454 MPa and 5.1 MPa·m1/2, respectively, for 40% (w/w) BAS/SiC composites. SiC grain pullout, crack deflection, and crack bridging were main toughening mechanisms for the sintered composites.     

Study on the fabrication and characterization of ZTA-SiCw-TiC polyphase ceramics

Novel ZTA/Al₂O₃-SiC_w-TiC polyphase ceramics were fabricated by hot pressing techniques. Phase transformation toughening, particle dispersion and whisker reinforcement have obviously superposed strengthening and toughening effects. It is observed that ZTA-20SiC_w-20TiC has better comprehensive mechanical properties compared with Al₂O₃-20SiC_w-20TiC. For the optimum processing, the ZTA-20SiC_w-20TiC exhibited a flexural strength of 567MPa, a fracture toughness of 6.3MPa·m^0.5, a hardness of HRA93.6 and a relative density of ≥99.6 %. The tensile stress in matrix introduced by SiC whisker and TiC could be relaxed by the compress stress produced by tetragonal zirconia (ZrO₂(t)) transformation. TiC formed a continuous skeleton which prevented the grain growth of the matrix. The grain sizes of the matrix became finer with increasing TiC. The major fracture mode of the matrix was transcrystalline cleavage rupture. Supported by the Young Science Foundation of Shanghai Municipal Commission of Education(98QN55)     

Preparation and Dynamic Tensile Behavior of C200 Green Reactive Powder Concrete

A new type of green reactive powder concrete (GRPC) with compressive strength of 200 MPa is prepared by utilizing composite mineral admixtures, natural fine aggregates, and short and fine steel fibers. The quasi-static mechanical properties (mechanical strength, toughness, fracture energy and interfacial bonding strength) of GRPC specimens, cured in three different types of regimes, are investigated. The experimental results show that the mechanical properties of the C200 GRPC made with the powder binders that is composed of 40% of Portland cement, 25% of ultra fine slag, 25% of ultra fine fly ash and 10% of silica fume are better than the others'. The corresponding compressive strength, flexural strength and fracture energy are more than 200 MPa, and 30 000 J/ m2 respectively. The dynamic tensile behavior of the C200 GRPC is also investigated through the split Hopkinson pressure bar (SHPB) according to the spalling phenomenon. The dynamic testing results demonstrate that strain rate has an important effect on the dynamic tensile behavior of GRPC. With the increase of strain rate, its peak stress and relevant strain increase. The GRPC exhibits an excellent strain ratio stiffening effect under the dynamic tensile load with high strain ratio, resulting in a significant change of the fracture pattern.     

Effect of agarose content on microstructures and mechanical properties of porous silicon nitride ceramics produced by gelcasting

<正>Porous Si3N4 self-reinforce ceramics were prepared by gelcasting using agarose solutions. By changing the agarose content in the slurries, the porous silicon nitride ceramics with different porosities, α→β-Si3N4 phase transformation, and mechanical properties were obtained. When the agarose content changed from 0.2% to 0.8% (w/w, based on powder), the porosities increased from 10.3% to 21.4%, while the fracture strength decreased from 455 to 316 MPa and the fracture toughness decreased from 6.6 to 5.5 MPa·m1/2. Many fibrous β-Si3N4 grains grown from the internal wall of the round pores is the typical microstructure of the gelcasting porous silicon nitride ceramic. Both elongated β-Si3N4 grains and suitable interfacial bonding strength contributes to high fracture toughness by favoring crack deflection and bridging. The growth mechanisms of fibrous grains resulted from the synergy of solution-diffusion-reprecipitation and vapor-liquid-solid (VLS).     

Effects of agarose concentration and addition on the properties of gel-cast 3Y-ZrO2 green and sintered bodies

Using agarose as a gel agent to prepare ceramics is a suitable non-toxic gel-casting method. The effects of agarose concentration and addition amount on gel-cast 3Y-ZrO_2 green and sintered bodies were investigated. Green bodies were prepared by gel-casting using an agarose solution of a different agarose mass fraction including 3.0%, 3.5%, 4.0%, 4.5%, 5.0% and 5.5%with an added amount of agarose in the green body at a mass fraction of 0.7%, and using the agarose solution of a mass fraction of4.5% with a different amount of added agarose including 0.6%, 0.7%, 0.8%, 0.9%, and 1.0% in terms of mass fraction. The green bodies were sintered at 1 600 °C for 4 h. The relative density, linear shrinkage, and bending strength of the green bodies, and the density, microstructure, bending strength, and fracture toughness of sintered samples were characterized and analyzed. Results show that comprehensive properties of green bodies made with 4.5%(in terms of mass fraction) agarose solution added to an mass fraction of agarose in the slurry at 0.6% were the best, of which the bending strength was 3.14 MPa, the linear shrinkage was below 4.3%, and the relative density is 57.3%. For sintered bodies, the best fracture toughness was 5.63 MPa m~(1/2), and the optimal density was 5.88 g cm~(-3).     

细分散B_4C颗粒对Si_3N_4陶瓷的增强与增韧效应

本文通过对不同B4C含量的Si3N4陶瓷的力学性能研究,探讨了B4C相变对Si3N4陶瓷的强度和韧度的影响,分析了各种增强与增韧的机制,并用能量平衡理论讨论了强度和韧度增加的原因.结果表明,利用应力诱导相变效应,可以有效地提高Si3N4陶瓷的弯曲强度和断裂韧度.